1. Field of the Invention:
This invention relates to a reproducing apparatus which excels in dubbing characteristics.
2. Description of the Prior Art:
Still picture video recording systems (hereinafter call SV systems) record still picture video signals on magnetic discs or other information recording media. The discs or media may, for example, record a luminance signal within a high frequency zone and a color signal within a low frequency zone in a color-difference line sequence, as shown in FIG. 1 of the accompanying drawings, either in the form of a field recording covering just one field or in the form of a frame recording covering two fields.
In a reproducing apparatus, therefore, the color signal must be interpolated to have the line sequential color difference signals converted into concurrent color difference signals. Further, in field recording, the signal must be converted into a frame signal for the purpose of having an interlace display at a monitor. For the conversion, interpolation is generally carried out by averaging horizontal line signals. This method is highly advantageous as it gives improved resolution at the monitor.
In dubbing, however, the above-described interpolating method degrades the resolution. In a standard SV system, the line sequential color difference signals (B-Y and R-Y) have an arbitrary phase in the odd- and even-number fields. Further, in field recording, the signal is recorded in either an odd-number field or an even-number field. This shortcoming of the prior art is further described with reference to FIGS. 2A and 2B.
In FIGS. 2A and 2B, the illustrated system includes 0.5 H delay (DL) circuits 1 and 4, with reference symbol H denoting a horizontal period; switch circuits SW1 to SW4; and 1 H delay circuits 2, 5, and 6. These circuits are disposed within an output circuit of a reproducing apparatus which will be subsequently described.
FIG. 2A shows a luminance (Y) signal interpolation circuit. The switches SW1 and SW2 are arranged to be switched over to each other for every field. Accordingly, the input Y signal is produced after having been delayed by 1 H (horizonal period) for a first field. For a next field, the Y signal is skew compensated by the 0.5 H delay circuit 1 and is then averaged with the input and output signals of the next 1 H delay circuit 2 used. As a result, an interpolation signal delayed by 1.5 H is produced from the luminance (Y) signal interpolation circuit.
FIG. 2B shows a color (C) signal interpolation circuit. In this circuit, the switch SW3 and the 0.5 H delay circuit 4 are provided for skew compensation. The 1 H delay circuits 5 and 6 and the switch SW4 change the line sequential color difference signals into concurrent signals. More specifically, the incoming line sequential signals include R-Y and B-Y signals for every H period. Another color difference signal which does not include these signals is made into concurrent signals by averaging (interpolating) 0 H and 2 H signals. Therefore, the concurrent color difference signals are: EQU R-Y: 1 H, 1/2 (0 H+2 H), 1 H --- EQU B-Y: 1/2 (0 H+2 H), 1 H, 1/2 (0 H+2 H) ---
Accordingly, one of the color difference signals is always produced as an interpolated concurrent signal. Therefore, during the process of dubbing the luminance signal, the interpolated signal might be dubbed in reproducing the information which has been field recorded. Conversely, for the color signal, the interpolated color difference signal is always dubbed. With the dubbing repeated, therefore, the vertical resolution degrades in proportion to the number of repeated dubbings. In horizontal interpolation, the horizontal resolution is similarly degraded.
In having information recorded on a magnetic disc dubbed to another disc, the problem of time base variations arises. A time base variation caused by a motor and a time base variation caused by variations in loads on the disc and a magnetic head result in a small picture distortion in the horizontal direction of a reproduced picture. At present, this is corrected by the AFC characteristic of the display. However, if the time base variations become excessive as the dubbing is repeated, correction is no longer possible.
There is another problem with prior art systems. In the magnetic conversion system of the reproducing apparatus, deterioration of the S/N ratio of a reproduced modulated signal arises from AM noise resulting from a slight difference in touch between the magnetic disc and the magnetic head. This AM noise can be, for example, a sliding noise, the thermal noise of the magnetic head, modulation noise, etc.
The prior art also suffers from deterioration of a high frequency characteristic mainly in the recording and reproducing system, including the magnetic disc and the magnetic head.